The present disclosure generally relates to the field of fault detection. The present disclosure relates more specifically to fault detection in environmental control systems such as air handling units.
Air handling units (AHUs) are often controlled by a controller implementing a finite state machine control strategy. Such a control strategy defines the various states of operation of the AHU (e.g., a heating state, a cooling state, etc.) and includes logic for determining when to cause the AHU to switch states.
The AHU, as controlled by its controller, is typically configured to regulate the mixture of outdoor air and return air with mechanical cooling or heating to efficiently condition the air being supplied to the building space being served by the AHU. Accurate control depends on receiving accurate sensor data regarding a climate condition in the building space (e.g., a current temperature, a current humidity, etc.), outside the building, or within the AHU.
A number of faults may occur that adversely affect the operation of the AHU. For example, a sensor error (ranging from complete failure to excessive noise causing inaccuracies) can produce faulty controller operation and therefore faulty AHU operation. Errors may also be due to leaky or stuck dampers or valves, fan problems, or other mechanical issues.
U.S. Pat. No. 6,223,544 to Seem titled “Integrated Control and Fault Detection of HVAC Equipment,” issued May 1, 2001 (the '544 patent), which is incorporated herein by reference in its entirety, discloses a system for conducting fault detection in an environmental control system. The system of the '544 patent detects faults by comparing actual system performance to a model of the system, with the comparison producing a residual value indicative of whether the actual performance matches the model. In the '544 patent, thirteen residuals for conducting such a comparison are presented.